Existing and emerging consumer applications have created an increasing need for real-time three-dimensional (3D) imagers. These imaging devices, also commonly known as depth sensors or depth mappers, enable the remote measurement of distance (and often intensity) of each point on a target scene—so-called target scene depth—by illuminating the target scene with one or more optical beams and analyzing the reflected optical signal.
A commonly used technique for determining the distance to each point on the target scene involves sending an optical beam towards the target scene, followed by the measurement of the round-trip time, i.e. time-of-flight (ToF), taken by the optical beam as it travels from the source to target scene and back to a detector adjacent to the source.
Another commonly used technique is based on projecting a pattern of structured light onto a scene and capturing an image of the projected pattern. The distance to each point in the scene is derived from the local displacement of the pattern.
Target scene depth is measured for the points illuminated by the projected beams. Consequently, it is advantageous to increase the number of beams, either for higher lateral resolution or for a wider coverage of the target area. One method for increasing the resolution using a diffractive optical element (DOE) is described in United States Patent Application Publication 2016/0025993, whose disclosure is incorporated herein by reference.